Cutting tubular plastic extrusion

ABSTRACT

The disclosure relates to a process and apparatus for cutting extruded plastic tubes while avoiding excessive distortion of the tubes wherein a fluid pressure differential is created between the inside and outside of the tube on both sides of the cutting knife so as to keep the tube from collapsing under the pressure of the knife.

United States Patent 1 1 1 9 Bhatia 1 May 1, 1973 CUTTING TUBULARPLASTIC 2,802,530 8/1957 Kaufman ..s3/22 x EXTRUSION 3,567,088 3/1971Andersen "83/169 x [75] Inventor: Mahesh Bhatia, Woodside, NY. I

Primary ExammerJames M. Me1ster [73] Ass1gnee: Anchor Plastics Company,Inc., Att0mey Greene & Du"

Long Island City, NY.

[22] Filed: Oct. 12, 1971 [21] Appl. No.: 188,360 [57] ABSTRACT Thedisclosure relates to a process and apparatus for [52] U S Cl 83/5483/169 83/70} cutting extruded plastic tubes while avoiding excessive 51int 01. .:I:11:31:11: .3 ..B2 6d 3/16 the tubes wherein a fluid Pressure[58] Field of Search ..s3/54, 22, 14, 13, ferenfial is Created betweenthe inside and Outside of 3 9 70 the tube on both sides of the cuttingknife so as to keep the tube from collapsing under the pressure of [56]References Cited the knife.

UNITED STATES PATENTS 4 Claims, 2 Drawing Figures 1,997,843 4/l935Warrell ..83/22 X CUTTING TUBULAR PLASTIC EXTRUSION This inventionrelates to the process and apparatus for cutting tubular plasticextrusion products of the type which collapse under pressure or impactfrom a knife or saw.

With tubular plastic extrusions,. especially thinwalled tubularplastics, the tube collapses under the pressure of the cutting tool andmay be more or less permanently deformed by the pressure of the cuttingtool.

Among the objects of the invention is to provide a process and apparatusfor preventing the collpasing of tubular plastic extrusion products whencut by an impact tool.

The objects of the invention are attained by providing a pressuredifferential between the interior and the exterior of the tube, so as tohold the tube against collapsing. Thus, the tube is passed through twosubstantially air-tight chambers, one on each side of the cutting tool.As the cutting tool is moved to cut the tube, vacuum is applied to thechambers to hold the tube in expanded condition while the cutting toolis piercing the tube. Vacuum is applied to the entire surface or in theregion which is deformed by impact. Upon release of the vacuum, theportion of the tube which has been cut off is pushed through the vacuumchamber by the continuous uncut tubular extrusion.

For a complete understanding of the invention, reference is made to theaccompanying drawings illustrating a preferred embodiment, but it willbe understood that the invention may be otherwise embodied within thescope of the broader claims in the drawings:

FIG. 1 is a side view, somewhat diagrammatic, of an apparatus madeaccording to the invention.

FIG. 2 is a cross-sectional detail view taken on line 2-2 of FIG. 1.

The tubular product is formed by extrusion device 11 in known manner andis passed directly through cooling device 12. Cooling device 12 is shownonly diagrammatically and may include liquid or gaseous (air) cooling.

Tube 10 is positively forwarded by two or more takeoff belts 13,14 intothe chambers and 20'. The chambers 20 and 20' are similarly constructed,each being provided with flexible elastomeric gaskets 21, 21 22, 22, atthe entrance and exits, respectively. In a central portion of thechamber, jigs 23, 23 containing an opening 24, 24, suitably supported byrods 25, 25', 26, 26 so that the opening 24 or 24 is aligned with theopenings in gaskets 21, 22 and with the tube 10. Each chamber isprovided with a tubular outlet 27, 27' connected through valve 28 tovacuum chamber 31. Each chamber is also provided with a vent and valve29, 29 to release the vacuum. Vacuum chamber 31 acts as a vacuumreservoir to allow rapid vacuum cycles in chamber 20 and 20.

A suitable electronic control device 32 is provided to operate valves28, 29, 29', and the knife 30, so that the vacuum is momentarily appliedas the knife is about to cut the tube and so that the vacuum is releasedas soon as the tube has been cut. Such electronic control circuits arewell-known in the industry and are not described in detail here. Thevacuum chamber 31 may also be provided with a guage 34, relief valve 35,and valve connection 36 connecting to a vacuum pump (not shown), whichis also controlled by the electronic device 32. v

In operation, the tube 10, after cooling, is propelled by conveyor 13,14 into chambers20, 20'. After a predetermined length of tube has passedthrough chamber 20', cutting device 30 (knife or saw) is rotated andimmediately before it strikes the tube, vacuum is applied so that thetube does not collapse under the initial pressure of the cutting device.After the tube is cut, the vacuum is released so that the uncut portionof the tube coming from chamber 20 pushes the cut tube out of chamber20. As is known in the art, the length of tube allowed to passthrough/chamber 20 before the next cycle of the cutting knife can beregulated solely by a timing means or by some triggering device appliedto the free end of the tube passing out of chamber 20.

We claim:

1. In a process for making relatively thin-walled plastic tubular bodiesof predetermined length by extruding a continuous plastic tube andcutting the tube to the desired length, the improvement comprisingapplying a pressure differential to the tube at two closely spacedregions along the length thereof, to hold the tube against collapsingand cutting the tube while so held in the region between said twoclosely spaced regions.

2. The process as claimed in claim 1 wherein said pressure differentialis applied by applying a vacuum to the outside surface of the tube.

3. An apparatus for making finite lengths of relatively thin-walledplastic tubular bodies from a continuously extruded tube comprisingmeans for positively propelling the tube, a first and secondsubstantially airtight chambers, each having entrance and exit openingsfor the passage of said tubular bodies, means for simultaneouslyapplying a vacuum to said chambers, means for releasing the vacuum fromsaid chambers, and impact cutting means adapted to cut the tubeextending between the chambers.

4. The process as claimed in claim 1 wherein said tube is cut by impactwith a cutting tool, said pressure differential being applied to onlythose regions of the tube adjacent the portion which is deformed by theimpact of the cutting tool.

1. In a process for making relatively thin-walled plastic tubular bodiesof predetermined length by extruding a continuous plastic tube andcutting the tube to the desired length, the improvement comprisingapplying a pressure differential to the tube at two closely spacedregions along the length thereof, to hold the tube against collapsingand cutting the tube while so held in the region between said twoclosely spaced regions.
 2. The process as claimed in claim 1 whereinsaid pressure differential is applied by applying a vacuum to theoutside surface of the tube.
 3. An apparatus for making finite lengthsof relatively thin-walled plastic tubular bodies from a continuouslyextruded tube comprising means for positively propelling the tube, afirst and second substantially air-tight chambers, each having entranceand exit openings for the passage of said tubular bodies, means forsimultaneously applying a vacuum to said chambers, means for releasingthe vacuum from said chambers, and impact cutting means adapted to cutthe tube extending between the chambers.
 4. The process as claimed inclaim 1 wherein said tube is cut by impact with a cutting tool, saidpressure differential being applied to only those regions of the tubeadjacent the portion which is deformed by the impact of the cuttingtool.